a) Technical Field of the Invention
The present invention relates to a cold cathode tube for use in Liquid Crystal Display (LCD), and in particular, to a cold cathode tube in which the inner wall is coated with an ultra-violet (UV) light reflective film capable of reflecting ultraviolet light.
b) Description of the Prior Art
FIG. 1 shows a sectional view of a conventional cathode tube 1, which is a circular shape. The inner wall of the tube 11 is coated with InO2, which is an UV absorbing film 12. The inner side of the film 12 is then coated with a thin layer of fluorescent material 13. The tube 11 is filled with a small amount of a gas. The principle of a cathode tube is that voltage from an electric power source is applied across the tube and the electrical energy, via electron and photon to initiate the gas to release UV light. The light impinges against the fluorescent material 13 and is then converted to visible light and is emitted for application. This conventional cathode tube 1 is provided as a light source. However, due to its circular shape, the visible rays are emitted out in all direction. Such inherited exhaustion is due to the shape restriction of the cathode tube. As shown in FIG. 2, when it is used in LCD, the external side of the tube 1 must be mounted with a lampshade 14 with an open end corresponding to the light source panel 2.
The reflective function of the lampshade 14 allows the visible light to reflect to the light source panel 2 so as to increase the light output efficiency of the tube 1. However, the mounting of the lampshade 14 will increase the cost of production, and the entire cathode tube cannot be miniaturized. In addition, the emitted light energy will be lowered during the process of light reflection from the lamnpshade 14 to the light source panel 2. Due to the fact that the visible light will lose some of the energy as a result of the fluorescent agent layer 13. At the same time, the UV absorbing thin film 12 will absorb the unconverted UV such that the output energy within the tube 1 cannot effectively utilizes the energy within the tube. This will lower the light effectiveness of tube.
Further, the external diameter of the tube 1 is smaller than the height of the incident face 21 of the light source panel 2 so as to connect the lampshade 14 to the incident face 21 to lead light energy to the light source panel 2. This will restrict the tube and in turn, restrict the output light energy.
Accordingly, it is an object of the present invention to provide a cold cathode tube having a fluorescent material coated along the inner wall thereof and the tube being filled with a small amount of gas, characterized in that the inner wall of the tube is coated with a ultra-violet ray reflective film capable of reflecting ultra-violet light, and the light emission surface at the inner side of the ultra-violet light reflective film does not coat with a fluorescent material, and the remaining region of the light emission surface at the outer wall is coated with a visible light-reflective layer. In addition, the length of the parallel section of the tube can be extended to increase the light emission area, and thus the efficiency of light energy output is increased.
Yet another object of the present invention is to provide a cold cathode tube, wherein the flat board shaped light output face of the tube is extended with a parallel section connected with a circular arch-shaped section.
A further object of the present invention is to provide a cold cathode tube, wherein the length of the parallel section can be extended to increase the light emission area so as to increase the light energy output of the tube.
Other features and benefits of the present invention will become apparent from the detailed description with the accompanying drawings contained thereinafter.